1. Field of the Invention
The present invention relates generally to downhole oil well tools run on a pipe string, including impact or jarring type downhole oil well tools, and more particularly, to a fluid operated jarring tool and related methods of operation for use in well bores and wherein the tool has a bit or working end that jars downwardly and rotates when the bit is not subject to weight of the pipe string in order to prevent imprinting on the drilling surface.
2. General Background
In downhole well operation, there is a need for jarring or impact devices. For example, in workover operations using a pipe string such as coil tubing or snubbing equipment, it is necessary to provide downward jarring impact at the bottom of the string to enable the string to pass obstructions or restrictions (such as isolation packers, liners, etc.) or otherwise enter the well perforated zone. During fishing operations or other operations, such as paraffin scraping, it is sometimes necessary to apply upward and/or downward jarring or impact forces at the bottom of the string if the fishing tool or the like becomes stuck. This problem can be greater in inclined and in horizontal wells. In horizontal wells, the method and apparatus of the present invention can be used to overcome obstructions that can include friction between the drill string and well annulus. 11, through stem 25, through bit 14 to the drilling surface.
In prior U.S. Pat. No. 3,946,819, naming the applicant herein as patentee, there is disclosed a fluid operated well tool adapted to deliver downward jarring forces when the tool encounters obstructions. The tool of my prior U.S. Pat. No. 3,946,819, generally includes a housing with a tubular stem member telescopically received in the housing for relative reciprocal movement between a first terminal position and a second terminal position in response to fluid pressure in the housing. The lower portion of the housing is formed to define a downwardly facing hammer and the stem member includes an upwardly facing anvil which is positioned to be struck by the hammer. The tool includes a valve assembly that is responsive to predetermined movement of the stem member toward the second terminal position to relieve fluid pressure and permit the stem member to return to the first terminal position. When the valve assembly relieves fluid pressure, the hammer moves into abrupt striking contact with the anvil. The tool of prior U.S. Pat. No. 3,946,819, is effective in providing downward repetitive blows. The tool of the '819 patent will not produce upwardly directed blows.
In prior U.S. Pat. No. 4,462,471, naming the applicant herein as patentee, there is provided a bidirectional fluid operated jarring apparatus that produces jarring forces in either the upward or downward direction. The jarring apparatus was used to provide upward or downward impact forces as desired downhole without removing the tool from the well bore for modification. The device provides downward jarring forces when the tool is in compression, as when pipe weight is being applied downwardly on the tool, and produces strong upward forces when is in tension, as when the tool is being pulled upwardly.
In U.S. Pat. No. 4,462,471, there is disclosed a jarring or drilling mechanism that may be adapted to provide upward and downward blows. The mechanism of the '471 patent includes a housing having opposed axially spaced apart hammer surfaces slidingly mounted within the housing between the anvil surfaces. A spring is provided for urging the hammer upwardly.
In general, the mechanism of the '471 patent operates by fluid pressure acting on the valve and hammer to urge the valve and hammer axially downwardly until the downward movement of the valve is stopped, preferably by the full compression of the valve spring. When the downward movement of the valve stops, the seal between the valve and the hammer is broken and the valve moves axially upwardly.
The direction jarring of the mechanism of the '471 patent is determined by the relationship between the fluid pressure and the strength of the spring that urges the hammer upwardly. Normally, the mechanism is adapted for upward jarring. When the valve opens, the hammer moves upwardly to strike the downwardly facing anvil surface of the housing. The mechanism can be made to deliver a downward and upward blow by increasing the fluid pressure and decreasing the strength of the spring that urges the hammer upwardly. When the mechanism is so arranged, the downward momentum of the hammer is increased such that the hammer strikes the upwardly facing anvil of the housing prior to being urged upwardly to strike the downwardly facing anvil surface.
One of the problems with these prior art devices is the fact that during impact drilling, imprinting on the drilling surface can occur reducing or preventing penetration. The present invention rotates the working end, e.g. a drill bit, during impact drilling. With the present invention, by rotating the bit when it is not subject to weight of the pipe string, very little energy is required. As compared to rotating the bit when it is weighted, this "unweighted" rotation slows bit wear. Thus, impact drilling can proceed with a constant movement or rotation of the bit to prevent imprinting on the drilling surface.
Another problem relating to controlling the amount of the weight on a drill bit. Presently, drill pipe weight is the typical method of controlling the weight on a drill bit. In one embodiment of the present invention, a coiled spring, disk spring or other bias means is placed in the tool in such a way that a predetermined amount of force or load could be applied to the bit. This force will vary some what, increasing as the tool body moves downward. Thus, two forces of downward force can be applied to the bit. The first would be the weight of the tubing on the tool, controlled by the operator at the surface of the well, and the second would be the predetermined constant load imposed on the bit through the "bias means", preferably a coil spring or disk spring.
During certain down hole impact drilling operations, large amounts of fluid are sometimes required to accomplish the task. For example, when acidizing or fracturing a well or when operating in a large annulus, the fluid velocity must be maintained to carry cuttings to the surface. Often nitrogen is introduced into this fluid in the form of gas, sometimes being mixed with a foaming surfactant. Nitrogen is a gas with high energy and has a very high rate of expansion.
Impact tools operate on a fixed volume of fluid per stroke, the higher the volume the faster the impact cycle. The impact cycle of these tools depends on the near total evacuation of the pressure in the chamber to obtain a clean blow. There is therefore a point where the amount of fluid being pumped through a tool exceeds the tool's ability to exhaust the chamber (volumetric efficiency). When this point is reached, the tool chamber will maintain a positive pressure differential and the impact will be cushioned much like the action of an automobile shock absorber. This condition is especially prevalent when a highly expansive gas such as nitrogen enters the chamber. It is therefore advantageous and desirable to devise a method that will allow one to maintain a high fluid volume while at the same time allowing the impact tool to perform at an optimum rate.
This is accomplished with the method and apparatus of the present invention by installing choke holes at the port or exit and laterally of the impact tool's chamber. These choke holes can be sized to pass as much fluid as desired and yet maintain the optimum fluid value for the tool's operation. The fluid volume must exceed the flow capability of the chokes before the chamber of the tool can pressure to the point of tool operation. For example, if it is established that a given tool's optimum operating fluid rate is 30 gpm but 60 gpm is required for lifting, then the choke would be designed to pass 30 gpm at the tool's optimum operating pressure. All fluid exits the tool via the center bore and out the bottom, aiding the lifting operation.